Ballistic missiles were first used in World War II. During the Cold War, the Nazi wartime designs were used to develop intercontinental ballistic missiles (ICBMs). These have a range of 5.500 km. (Source: Wikipedia).
Alongside, we have RADAR development. The RADAR for ICBMs are called "Early Warning Systems", and should theoretically tend to have global reach.
In this interview U.S. General Thomson refers to missile defense: "First, it was Air Forces and Air Defenses and we built Air Defenses". "Ballistic missiles came online, we understand what ballistic missiles is and we built defenses". On hypersonic missiles: "it is a challenge, we have done this before, we can do it again."
Countries and allied structures have electromagnetic surveillance systems or sensors, including RADAR, to protect land, sea, air, and space. These include the missile warning system. Defense communications (e.g. in the ELF/VLF range) may be included. All sensors are combined by creating an electromagnetic or electronic fence in order to provide a consolidated output for space situational awareness (SPA).
A Lockheed Martin paper (2015) explains the system: https://amostech.com/TechnicalPapers/2015/SSA/Haimerl.pdf
Videos (including promotional video):
https://www.youtube.com/watch?v=DxCKjV3u9TA
https://www.youtube.com/watch?v=NNCmWdCOD9A